In recent years, stereo camera apparatuses that measure the distance to a subject using a plurality of cameras have been used in vehicles such as cars. When using a stereo camera to detect a three-dimensional object and measure distance, it is not always easy to detect a three-dimensional object from a plurality of actually captured images when the images are complex. Therefore, methods have been proposed to calculate a distance distribution across the entire captured image and to discriminate obstacles on the basis of information on the distance distribution, using a three-dimensional object detection apparatus (for example, see patent literature (PTL) 1).